There are known tumble dryers of the type comprising a casing supporting an enveloping wall inside which a rotating drum with perforated walls is installed for containing clothes to be dried, and air-heating means in combination with a turbine or the like to impel hot air in a radial direction of the drum through its perforated walls towards an exhaust duct through which the hot air from the drum is expelled outside. An air filter is arranged in said exhaust duct to retain the fluff released by the clothes and suspended in the hot air. Tumble dryers of another type are also known, for instance through U.S. Pat. No. 4,593,481, wherein the air-heating means and the turbine are arranged to at least partially impel hot air in the axial direction of the drum and towards the exhaust duct wherein the filter is located. In both types of tumble dryer, the fluff resulting from the filtering of hot air gradually builds up in the filter, and this hinders air circulation, diminishes the efficiency of the dryer and is detrimental to the mechanical elements, so that it is recommended that the filter be cleaned at least after two or three tumbling cycles. The filter is generally accessible and/or removable to proceed to its cleaning, but this is a time-consuming operation. In domestic applications, wherein there is usually one single tumble dryer carrying out an average of one tumbling cycle per day, the time required to clean the filter is readily acceptable. However, in industrial applications wherein there can be a set of several tumble dryers, each carrying out up to sixteen or more tumbling cycles per working shift, the time required for the repeated cleaning of the filters and the economic cost it involves are hardly assumable.
Patents EP-A-0163879 and DE-A-3817849 describe different dry-cleaning machines, which are also subject to the fluff problem, endowed with suction nozzles connected to an external suctioning static installation. The internal suction nozzles are connected to mechanisms that move them in a proximity relationship with the filter while the suction flow is on to dislodge and remove the fluff from the filter. This solution involves a large economic cost, since it is mechanically complex and requires an external vacuum-generating installation and an external network of fixed suction ducts. In addition, the suction nozzle-moving mechanisms are immediately adjacent to the filter wherein the fluff builds up, and they can be negatively affected by the fluff build-up.
Patent JP-A-7-163793 describes a domestic tumble dryer provided with a filtering device designed in such a way that it can be manually cleaned using an external vacuum cleaner of a conventional type without the need to disassemble the filter, wherein the filtering device is arranged in the bottom of the drum and access thereto by means of the suction nozzle of the vacuum cleaner is carried out through the load/unload door of the drum. One inconvenience is that carrying out the filter cleaning first requires accessing the filter by means of the suction nozzle through the open load/unload door when the drum is empty and then go through the various areas of the filter with the nozzle, which takes up a time during which other operations, such as the loading/unloading of clothes into/from the drum cannot be carried out.
U.S. Pat. No. 7,325,332 discloses a domestic tumble dryer wherein the filtering device includes a cavity with slots wherein a filter is removably installed. With the tumble dryer, a connecting unit is provided that can be located in said slots of the device in place of the filter when the latter has been removed, and said connecting unit is configured to be connected to the suction nozzle of a vacuum cleaner for cleaning the hot air exhaust duct of the tumble dryer. Access to the filtering device is carried out through the load/unload door of the drum when it is open, and when the filter has been removed, whereby the cleaning operation must be carried out consuming some time while the tumbling cycle is stopped or between two tumbling cycles.
There are known tumble dryers provided with a filter that can be easily removed through an access different from the load/unload door of the drum, and the removed filter can be cleaned by any means, obviously including an external vacuum cleaner. However, the need to extract the filter to effect its cleaning requires a relatively long time and involves the risk of scattering the fluff in the surrounding environment.
U.S. Pat. No. 5,535,478 discloses a suction device provided with a flexible suction nozzle for cleaning a cavity wherein there is housed the air filter of a domestic tumble dryer from which the filter has been previously removed. The suction nozzle is especially configured with rough edges and lateral and end suction openings to carry out a dual function: a scraping action of the cavity walls by means of said rough edges in order to dislodge the fluff attached to them and a suctioning function by means of said lateral and end openings to remove the detached fluff. One inconvenience is that the suction nozzle of the suction device has a specific design corresponding to the cavity of the filter of the tumble dryer and, in addition, it is required the previous withdrawal of the filter for it to be able to carry out the cleaning of the cavity where the filter is housed.
International patent application WO-A-2008086875 discloses a domestic tumble dryer provided with an air filter connected to a vibrating device that can be turned on to detach the fluff from the filter. The detached fluff falls by gravity into a container that can be periodically removed to empty it. The activation of the vibrating device must be carried out when the tumbling airflow is stopped, since the detached fluff would otherwise be impelled again by the airflow against the filter. The need to remove the container from the tumble dryer for cleaning has the inconveniences described above in relation to the need of removing the filter.
Since they do not have the space limitation of domestic tumble dryers, industrial tumble dryers generally have a casing with three overlaying regions: an upper region wherein air-heating means are housed, a middle region wherein the tumbling drum is located, and a lower region, wherein a low-pressure chamber through which hot air circulates coming from said tumbling drum is located and also having means to create said low pressure so as to cause the circulation of air towards an exhaust, and a filtering device in an air passage towards the low-pressure chamber. Tumble dryers of this type are known wherein the filtering device has the shape of a drawer provided with filtering walls where the air circulates from the inside out, so that the fluff is retained within the drawer. This drawer can be removed to clean the built-up fluff from the inner surfaces of the filtering walls. This device has, however, the inconvenience of consuming time and the risk of scattering fluff in the surrounding environment.